Electromyography (EMG) is a technique for evaluating and recording the electrical activity produced by
skeletal muscles.
EMG is performed using an
instrument called an electromyograph to produce a record called an electromyogram. An electromyograph detects the
electric potential
The electric potential (also called the ''electric field potential'', potential drop, the electrostatic potential) is defined as the amount of work energy needed to move a unit of electric charge from a reference point to the specific point in ...
generated by muscle
cells when these cells are electrically or neurologically activated. The signals can be analyzed to detect abnormalities, activation level, or recruitment order, or to analyze the
biomechanics of human or animal movement. Needle EMG is an
electrodiagnostic medicine
Electrodiagnosis (EDX) is a method of medical diagnosis that obtains information about diseases by passively recording the electrical activity of body parts (that is, their natural electrophysiology) or by measuring their response to external elect ...
technique commonly used by neurologists. Surface EMG is a non-medical procedure used to assess muscle activation by several professionals, including physiotherapists, kinesiologists and biomedical engineers. In Computer Science, EMG is also used as middleware in
gesture recognition
Gesture recognition is a topic in computer science and language technology with the goal of interpreting human gestures via mathematical algorithms. It is a subdiscipline of computer vision. Gestures can originate from any bodily motion or sta ...
towards allowing the input of physical action to a computer as a form of
human-computer interaction.
Clinical uses
EMG testing has a variety of clinical and biomedical applications. Needle EMG is used as a diagnostics tool for identifying
neuromuscular diseases
A neuromuscular disease is any disease affecting the peripheral nervous system (PNS), the neuromuscular junction, or skeletal muscle, all of which are components of the motor unit. Damage to any of these structures can cause muscle atrophy and weak ...
, or as a research tool for studying
kinesiology
Kinesiology () is the scientific study of human body movement. Kinesiology addresses physiological, anatomical, biomechanical, pathological, neuropsychological principles and mechanisms of movement. Applications of kinesiology to human health ...
, and disorders of motor control. EMG signals are sometimes used to guide
botulinum toxin
Botulinum toxin, or botulinum neurotoxin (BoNT), is a neurotoxic protein produced by the bacterium ''Clostridium botulinum'' and related species. It prevents the release of the neurotransmitter acetylcholine from axon endings at the neuromusc ...
or phenol injections into muscles. Surface EMG is used for functional diagnosis and during instrumental motion analysis. EMG signals are also used as a control signal for
prosthetic devices such as prosthetic hands, arms and lower limbs.
An
acceleromyograph
An acceleromyograph is a piezoelectric myograph, used to measure the force produced by a muscle after it has undergone nerve stimulation. Acceleromyographs may be used, during anaesthesia when muscle relaxants are administered, to measure the dep ...
may be used for
neuromuscular monitoring In anesthesia, neuromuscular blocking agents may be required to facilitate Tracheal intubation, endotracheal intubation and provide optimal surgical conditions. When neuromuscular blocking agents are administered, neuromuscular function of the pati ...
in general anesthesia with
neuromuscular-blocking drugs, in order to avoid
postoperative residual curarization
Postoperative residual curarization (PORC) or residual neuromuscular blockade (RNMB) is a residual paresis after emergence from general anesthesia that may occur with the use of neuromuscular-blocking drugs. Today residual neuromuscular blockade ...
(PORC).
Except in the case of some purely primary myopathic conditions EMG is usually performed with another
electrodiagnostic medicine
Electrodiagnosis (EDX) is a method of medical diagnosis that obtains information about diseases by passively recording the electrical activity of body parts (that is, their natural electrophysiology) or by measuring their response to external elect ...
test that measures the conducting function of nerves. This is called
nerve conduction studies (NCS). Needle EMG and NCSs are typically indicated when there is pain in the limbs, weakness from spinal
nerve compression
Nerve compression syndrome, or compression neuropathy, or nerve entrapment syndrome, is a medical condition caused by direct pressure on a nerve. It is known colloquially as a ''trapped nerve'', though this may also refer to nerve root compress ...
, or concern about some other neurologic injury or disorder.
[, which cites
*
* ] Spinal nerve injury does not cause neck, mid back pain or
low back pain, and for this reason, evidence has not shown EMG or NCS to be helpful in diagnosing causes of axial lumbar pain, thoracic pain, or
cervical spine pain.
Needle EMG may aid with the diagnosis of nerve compression or injury (such as
carpal tunnel syndrome
Carpal tunnel syndrome (CTS) is the collection of symptoms and signs associated with median neuropathy at the carpal tunnel. Most CTS is related to idiopathic compression of the median nerve as it travels through the wrist at the carpal tunn ...
), nerve root injury (such as sciatica), and with other problems of the muscles or nerves. Less common medical conditions include
amyotrophic lateral sclerosis
Amyotrophic lateral sclerosis (ALS), also known as motor neuron disease (MND) or Lou Gehrig's disease, is a neurodegenerative disease that results in the progressive loss of motor neurons that control voluntary muscles. ALS is the most comm ...
,
myasthenia gravis
Myasthenia gravis (MG) is a long-term neuromuscular junction disease that leads to varying degrees of skeletal muscle weakness. The most commonly affected muscles are those of the eyes, face, and swallowing. It can result in double vision, dro ...
, and
muscular dystrophy
Muscular dystrophies (MD) are a genetically and clinically heterogeneous group of rare neuromuscular diseases that cause progressive weakness and breakdown of skeletal muscles over time. The disorders differ as to which muscles are primarily affe ...
.
Surface EMG, conversely, is not used for diagnostic purposes.
Technique
Skin preparation and risks
The first step before insertion of the needle electrode is skin preparation. This typically involves simply cleaning the skin with an alcohol pad.
The actual placement of the needle electrode can be difficult and depends on a number of factors, such as specific muscle selection and the size of that muscle. Proper needle EMG placement is very important for accurate representation of the
muscle
Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...
of interest, although EMG is more effective on superficial muscles as it is unable to bypass the action potentials of superficial muscles and detect deeper muscles. Also, the more
body fat an individual has, the weaker the EMG signal. When placing the EMG sensor, the ideal location is at the belly of the muscle: the longitudinal midline. The belly of the muscle can also be thought of as in-between the motor point (middle) of the muscle and the tendonus insertion point.
Cardiac pacemakers and implanted cardiac defibrillators (ICDs) are used increasingly in clinical practice, and no evidence exists indicating that performing routine electrodiagnostic studies on patients with these devices pose a safety hazard. However, there are theoretical concerns that electrical impulses of nerve conduction studies (NCS) could be erroneously sensed by devices and result in unintended inhibition or triggering of output or reprogramming of the device. In general, the closer the stimulation site is to the pacemaker and pacing leads, the greater the chance for inducing a voltage of sufficient amplitude to inhibit the pacemaker. Despite such concerns, no immediate or delayed adverse effects have been reported with routine NCS.
No known contraindications exist for performing needle EMG or NCS on pregnant patients. Additionally, no complications from these procedures have been reported in the literature. Evoked potential testing, likewise, has not been reported to cause any problems when it is performed during pregnancy.
Patients with
lymphedema
Lymphedema, also known as lymphoedema and lymphatic edema, is a condition of localized swelling caused by a compromised lymphatic system. The lymphatic system functions as a critical portion of the body's immune system and returns interstitial fl ...
or patients at risk for lymphedema are routinely cautioned to avoid percutaneous procedures in the affected extremity, namely venipuncture, to prevent development or worsening of lymphedema or cellulitis. Despite the potential risk, the evidence for such complications subsequent to venipuncture is limited. No published reports exist of cellulitis, infection, or other complications related to EMG performed in the setting of lymphedema or prior lymph node dissection. However, given the unknown risk of cellulitis in patients with lymphedema, reasonable caution should be exercised in performing needle examinations in lymphedematous regions to avoid complications. In patients with gross edema and taut skin, skin puncture by needle electrodes may result in chronic weeping of serous fluid. The potential bacterial media of such serous fluid and the violation of skin integrity may increase the risk of cellulitis. Before proceeding, the physician should weigh the potential risks of performing the study with the need to obtain the information gained.
Surface and intramuscular EMG recording electrodes
There are two kinds of EMG: surface EMG and intramuscular EMG. Surface EMG assesses muscle function by recording muscle activity from the surface above the muscle on the skin. Surface EMG can be recorded by a pair of electrodes or by a more complex array of multiple electrodes. More than one electrode is needed because EMG recordings display the potential difference (voltage difference) between two separate electrodes. Limitations of this approach are the fact that surface electrode recordings are restricted to superficial muscles, are influenced by the depth of the subcutaneous tissue at the site of the recording which can be highly variable depending on the weight of a patient, and cannot reliably discriminate between the discharges of adjacent muscles. Specific electrode placements and functional tests have been developed to minimize this risk, thus providing reliable examinations.
Intramuscular EMG can be performed using a variety of different types of recording electrodes. The simplest approach is a monopolar needle electrode. This can be a fine wire inserted into a muscle with a surface electrode as a reference; or two fine wires inserted into muscle referenced to each other. Most commonly fine wire recordings are for research or kinesiology studies. Diagnostic monopolar EMG electrodes are typically insulated and stiff enough to penetrate skin, with only the tip exposed using a surface electrode for reference. Needles for injecting therapeutic botulinum toxin or phenol are typically monopolar electrodes that use a surface reference, in this case, however, the metal shaft of a hypodermic needle, insulated so that only the tip is exposed, is used both to record signals and to inject. Slightly more complex in design is the concentric needle electrode. These needles have a fine wire, embedded in a layer of insulation that fills the barrel of a hypodermic needle, that has an exposed shaft, and the shaft serves as the reference electrode. The exposed tip of the fine wire serves as the active electrode. As a result of this configuration, signals tend to be smaller when recorded from a concentric electrode than when recorded from a monopolar electrode and they are more resistant to electrical artifacts from tissue and measurements tend to be somewhat more reliable. However, because the shaft is exposed throughout its length, superficial muscle activity can contaminate the recording of deeper muscles. Single fiber EMG needle electrodes are designed to have very tiny recording areas, and allow for the discharges of individual muscle fibers to be discriminated.
To perform intramuscular EMG, typically either a monopolar or concentric needle electrode is inserted through the skin into the muscle tissue. The needle is then moved to multiple spots within a relaxed muscle to evaluate both insertional activity and resting activity in the muscle. Normal muscles exhibit a brief burst of muscle fiber activation when stimulated by needle movement, but this rarely lasts more than 100ms. The two most common pathologic types of resting activity in muscle are fasciculation and fibrillation potentials. A fasciculation potential is an involuntary activation of a
motor unit
A motor unit is made up of a motor neuron and all of the skeletal muscle fibers innervated by the neuron's axon terminals, including the neuromuscular junctions between the neuron and the fibres. Groups of motor units often work together as a mot ...
within the muscle, sometimes visible with the naked eye as a muscle twitch or by surface electrodes. Fibrillations, however, are detected only by needle EMG, and represent the isolated activation of individual muscle fibers, usually as the result of nerve or muscle disease. Often, fibrillations are triggered by needle movement (insertional activity) and persist for several seconds or more after the movement ceases.
After assessing resting and insertional activity, the electromyographer assess the activity of muscle during voluntary contraction. The shape, size, and frequency of the resulting electrical signals are judged. Then the electrode is retracted a few millimetres, and again the activity is analyzed. This is repeated, sometimes until data on 10–20 motor units have been collected in order to draw conclusions about motor unit function. Each electrode track gives only a very local picture of the activity of the whole muscle. Because skeletal muscles differ in the inner structure, the electrode has to be placed at various locations to obtain an accurate study.
Single fiber electromyography assesses the delay between the contractions of individual muscle fibers within a motor unit and is a sensitive test for dysfunction of the neuromuscular junction caused by drugs, poisons, or diseases such as myasthenia gravis. The technique is complicated and typically performed only by individuals with special advanced training.
Surface EMG is used in a number of settings; for example, in the physiotherapy clinic, muscle activation is monitored using surface EMG and patients have an auditory or visual stimulus to help them know when they are activating the muscle (biofeedback). A review of the literature on surface EMG published in 2008, concluded that surface EMG may be useful to detect the presence of neuromuscular disease (level C rating, class III data), but there are insufficient data to support its utility for distinguishing between neuropathic and myopathic conditions or for the diagnosis of specific neuromuscular diseases. EMGs may be useful for additional study of fatigue associated with post-poliomyelitis syndrome and electromechanical function in myotonic dystrophy (level C rating, class III data).
Recently, with the rise of technology in sports, sEMG has become an area of focus for coaches to reduce the incidence of soft tissue injury and improve player performance
Athos a Silicon Valley startup, has led the way as the only company to have thei
measurements validated as accurate and reliablecompared to a medical grade sEMG system.
Certain US states limit the performance of needle EMG by nonphysicians. New Jersey declared that it cannot be delegated to a physician's assistant. Michigan has passed legislation saying needle EMG is the practice of medicine. Special training in diagnosing medical diseases with EMG is required only in residency and fellowship programs in neurology, clinical neurophysiology, neuromuscular medicine, and physical medicine and rehabilitation. There are certain subspecialists in otolaryngology who have had selective training in performing EMG of the laryngeal muscles, and subspecialists in urology, obstetrics and gynecology who have had selective training in performing EMG of muscles controlling bowel and bladder function.
Maximal voluntary contraction
One basic function of EMG is to see how well a muscle can be activated. The most common way that can be determined is by performing a
maximal voluntary contraction (MVC) of the muscle that is being tested.
Muscle force, which is measured mechanically, typically correlates highly with measures of EMG activation of muscle. Most commonly this is assessed with surface electrodes, but it should be recognized that these typically record only from muscle fibers in close proximity to the surface.
Several analytical methods for determining muscle activation are commonly used depending on the application. The use of mean EMG activation or the peak contraction value is a debated topic. Most studies commonly use the
maximal voluntary contraction as a means of analyzing peak force and force generated by target muscles. According to the article "Peak and average rectified EMG measures: Which method of data reduction should be used for assessing core training exercises?", it was concluded that the “average rectified EMG data (ARV) is significantly less variable when measuring the muscle activity of the core musculature compared to the peak EMG variable.” Therefore, these researchers would suggest that “ARV EMG data should be recorded alongside the peak EMG measure when assessing core exercises.” Providing the reader with both sets of data would result in enhanced validity of the study and potentially eradicate the contradictions within the research.
Other measurements
EMG can also be used for indicating the amount of fatigue in a muscle. The following changes in the EMG signal can signify
muscle fatigue: an increase in the mean absolute value of the signal, increase in the
amplitude
The amplitude of a periodic variable is a measure of its change in a single period (such as time or spatial period). The amplitude of a non-periodic signal is its magnitude compared with a reference value. There are various definitions of amplit ...
and duration of the muscle action potential and an overall shift to lower frequencies. Monitoring the changes of different frequency changes the most common way of using EMG to determine levels of fatigue. The lower conduction velocities enable the slower
motor neuron
A motor neuron (or motoneuron or efferent neuron) is a neuron whose cell body is located in the motor cortex, brainstem or the spinal cord, and whose axon (fiber) projects to the spinal cord or outside of the spinal cord to directly or indirectl ...
s to remain active.
A
motor unit
A motor unit is made up of a motor neuron and all of the skeletal muscle fibers innervated by the neuron's axon terminals, including the neuromuscular junctions between the neuron and the fibres. Groups of motor units often work together as a mot ...
is defined as one motor
neuron
A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. N ...
and all of the
muscle fibers
A muscle cell is also known as a myocyte when referring to either a cardiac muscle cell (cardiomyocyte), or a smooth muscle cell as these are both small cells. A skeletal muscle cell is long and threadlike with many nuclei and is called a muscl ...
it innervates. When a motor unit fires, the impulse (called an
action potential
An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, ...
) is carried down the motor neuron to the muscle. The area where the nerve contacts the muscle is called the
neuromuscular junction
A neuromuscular junction (or myoneural junction) is a chemical synapse between a motor neuron and a muscle fiber.
It allows the motor neuron to transmit a signal to the muscle fiber, causing muscle contraction.
Muscles require innervation to ...
, or the
motor end plate
A neuromuscular junction (or myoneural junction) is a chemical synapse between a motor neuron and a muscle fiber.
It allows the motor neuron to transmit a signal to the muscle fiber, causing muscle contraction.
Muscles require innervation to ...
. After the action potential is transmitted across the neuromuscular junction, an action potential is elicited in all of the innervated muscle fibers of that particular motor unit. The sum of all this electrical activity is known as a motor unit action potential (MUAP). This electrophysiologic activity from multiple motor units is the signal typically evaluated during an EMG. The composition of the motor unit, the number of muscle fibres per motor unit, the metabolic type of muscle fibres and many other factors affect the shape of the motor unit potentials in the myogram.
Nerve conduction testing is also often done at the same time as an EMG to diagnose neurological diseases.
Some patients can find the procedure somewhat painful, whereas others experience only a small amount of discomfort when the needle is inserted. The muscle or muscles being tested may be slightly sore for a day or two after the procedure.
EMG signal decomposition
EMG signals are essentially made up of superimposed motor unit action potentials (MUAPs) from several motor units. For a thorough analysis, the measured EMG signals can be
decomposed into their constituent MUAPs. MUAPs from different motor units tend to have different characteristic shapes, while MUAPs recorded by the same electrode from the same motor unit are typically similar. Notably MUAP size and shape depend on where the electrode is located with respect to the fibers and so can appear to be different if the electrode moves position. EMG decomposition is non-trivial, although many methods have been proposed.
EMG signal processing
Rectification is the translation of the raw EMG signal to a signal with a single
polarity
Polarity may refer to:
Science
*Electrical polarity, direction of electrical current
*Polarity (mutual inductance), the relationship between components such as transformer windings
* Polarity (projective geometry), in mathematics, a duality of ord ...
, usually positive. The purpose of rectifying the signal is to ensure the signal does not average to zero, due to the raw EMG signal having positive and negative components. Two types of rectification are used: full-wave and half-wave rectification. Full-wave rectification adds the EMG signal below the baseline to the signal above the baseline to make a conditioned signal that is all positive. If the baseline is zero, this is equivalent to taking the
absolute value
In mathematics, the absolute value or modulus of a real number x, is the non-negative value without regard to its sign. Namely, , x, =x if is a positive number, and , x, =-x if x is negative (in which case negating x makes -x positive), an ...
of the signal. This is the preferred method of rectification because it conserves all of the signal energy for analysis. Half-wave rectification discards the portion of the EMG signal that is below the baseline. In doing so, the average of the data is no longer zero therefore it can be used in statistical analyses.
Limitations
Needle EMG used in clinical settings has practical applications such as helping to discover disease. Needle EMG has limitations, however, in that it does involve voluntary activation of muscle, and as such is less informative in patients unwilling or unable to cooperate, children and infants, and in individuals with paralysis. Surface EMG can have limited applications due to inherent problems associated with surface EMG. Adipose tissue (fat) can affect EMG recordings. Studies show that as adipose tissue increased the active muscle directly below the surface decreased. As adipose tissue increased, the amplitude of the surface EMG signal directly above the center of the active muscle decreased. EMG signal recordings are typically more accurate with individuals who have lower body fat, and more compliant skin, such as young people when compared to old. Muscle cross talk occurs when the EMG signal from one muscle interferes with that of another limiting reliability of the signal of the muscle being tested. Surface EMG is limited due to lack of deep muscles reliability. Deep muscles require intramuscular wires that are intrusive and painful in order to achieve an EMG signal. Surface EMG can measure only superficial muscles and even then it is hard to narrow down the signal to a single muscle.
Electrical characteristics
The electrical source is the muscle
membrane potential
Membrane potential (also transmembrane potential or membrane voltage) is the difference in electric potential between the interior and the exterior of a biological cell. That is, there is a difference in the energy required for electric charges ...
of about –90 mV. Measured EMG potentials range between less than 50 μV and up to 30 mV, depending on the muscle under observation.
Typical repetition rate of muscle
motor unit
A motor unit is made up of a motor neuron and all of the skeletal muscle fibers innervated by the neuron's axon terminals, including the neuromuscular junctions between the neuron and the fibres. Groups of motor units often work together as a mot ...
firing is about 7–20 Hz, depending on the size of the muscle (eye muscles versus seat (gluteal) muscles), previous axonal damage and other factors. Damage to motor units can be expected at ranges between 450 and 780 mV.
Procedure outcomes
Normal results
Muscle tissue at rest is normally electrically inactive. After the electrical activity caused by the irritation of needle insertion subsides, the electromyograph should detect no abnormal spontaneous activity (i.e., a muscle at rest should be electrically silent, with the exception of the area of the
neuromuscular junction
A neuromuscular junction (or myoneural junction) is a chemical synapse between a motor neuron and a muscle fiber.
It allows the motor neuron to transmit a signal to the muscle fiber, causing muscle contraction.
Muscles require innervation to ...
, which is, under normal circumstances, very spontaneously active). When the muscle is voluntarily contracted,
action potentials begin to appear. As the strength of the muscle contraction is increased, more and more muscle fibers produce action potentials. When the muscle is fully contracted, there should appear a disorderly group of action potentials of varying rates and amplitudes (a complete recruitment and interference pattern).
Abnormal results
EMG findings vary with the type of disorder, the duration of the problem, the age of the patient, the degree to which the patient can be cooperative, the type of needle electrode used to study the patient, and sampling error in terms of the number of areas studied within a single muscle and the number of muscles studied overall. Interpreting EMG findings is usually best done by an individual informed by a focused history and physical examination of the patient, and in conjunction with the results of other relevant diagnostic studies performed including most importantly, nerve conduction studies, but also, where appropriate, imaging studies such as MRI and ultrasound, muscle and nerve biopsy, muscle enzymes, and serologic studies.
Abnormal results may be caused by the following medical conditions (please note this is not an exhaustive list of conditions that can result in abnormal EMG studies):
Disorders of Muscle:
* Inflammatory myopathies
*
Polymyositis
Polymyositis (PM) is a type of chronic inflammation of the muscles (inflammatory myopathy) related to dermatomyositis and inclusion body myositis. Its name means "inflammation of many muscles" ('' poly-'' + '' myos-'' + ''-itis''). The inflammati ...
*
Dermatomyositis
Dermatomyositis (DM) is a long-term inflammatory disorder which affects skin and the muscles. Its symptoms are generally a skin rash and worsening muscle weakness over time. These may occur suddenly or develop over months. Other symptoms may inc ...
*
Inclusion body myopathy
Hereditary inclusion body myopathies (HIBM) are a group of rare genetic disorders which have different symptoms. Generally, they are neuromuscular disorders characterized by muscle weakness developing in young adults. Hereditary inclusion body m ...
*
Myotonia Congenita
* Muscular dystrophies:
*
Duchenne muscular dystrophy
*
Becker muscular dystrophy
Becker muscular dystrophy is an X-linked recessive inherited disorder characterized by slowly progressing muscle weakness of the legs and pelvis. It is a type of dystrophinopathy. This is caused by mutations in the dystrophin gene, which encodes ...
*
Facioscapulohumeral dystrophy
Facioscapulohumeral muscular dystrophy (FSHD) is a type of muscular dystrophy, a group of heritable diseases that cause degeneration of muscle and progressive weakness. Per the name, FSHD tends to sequentially weaken the muscles of the face, ...
*
Limb girdle muscular dystrophy
Limb may refer to:
Science and technology
*Limb (anatomy), an appendage of a human or animal
*Limb, a large or main branch of a tree
*Limb, in astronomy, the curved edge of the apparent disk of a celestial body, e.g. lunar limb
*Limb, in botany, ...
*
Centronuclear myopathy
*
Myotonic dystrophy
Myotonic dystrophy (DM) is a type of muscular dystrophy, a group of genetic disorders that cause progressive muscle loss and weakness. In DM, muscles are often unable to relax after contraction. Other manifestations may include cataracts, intel ...
* Mitochondrial myopathies
Disorders of the neuromuscular junction:
*
Myasthenia Gravis
Myasthenia gravis (MG) is a long-term neuromuscular junction disease that leads to varying degrees of skeletal muscle weakness. The most commonly affected muscles are those of the eyes, face, and swallowing. It can result in double vision, dro ...
*
Lambert–Eaton myasthenic syndrome
Lambert–Eaton myasthenic syndrome (LEMS) is a rare autoimmune disorder characterized by muscle weakness of the limbs.
Around 60% of those with LEMS have an underlying malignancy, most commonly small-cell lung cancer; it is therefore regarded ...
*
Botulism poisoning
*
Organophosphate
In organic chemistry, organophosphates (also known as phosphate esters, or OPEs) are a class of organophosphorus compounds with the general structure , a central phosphate molecule with alkyl or aromatic substituents. They can be considered a ...
poisoning
* Hypermagnesemia
* Hypocalcemia
Disorders of Nerves:
*
Carpal tunnel syndrome
Carpal tunnel syndrome (CTS) is the collection of symptoms and signs associated with median neuropathy at the carpal tunnel. Most CTS is related to idiopathic compression of the median nerve as it travels through the wrist at the carpal tunn ...
* Ulnar neuropathy at the elbow
* Radial nerve palsy (Saturday night palsy)
* Peroneal (fibular) nerve palsy
*
Diabetic neuropathy
Diabetic neuropathy is various types of nerve damage associated with diabetes mellitus. Symptoms depend on the site of nerve damage and can include motor changes such as weakness; sensory symptoms such as numbness, tingling, or pain; or autonomic c ...
* Alcohol related neuropathy
* Nutritional neuropathy
*
Amyloid neuropathy
* AIDP
* CIDP
*
Bell’s palsy
* Laryngeal neuropathy
* Pudendal neuropathy
* Femoral neuropathy
* Sciatic Neuropathy
* Tibial neuropathy
*
Tarsal tunnel syndrome
*
Charcot-Marie-Tooth syndrome
* Zoster neuropathy
* Oculomotor, Facial, vagal, trigeminal, glossopharyngeal, spinal accessory neuropathies
*
Hemifacial spasm Hemifacial spasm (HFS) is a rare neuromuscular disease characterized by irregular, involuntary muscle contractions (spasms) on one side (hemi-) of the face (-facial). The facial muscles are controlled by the facial nerve (seventh cranial nerve), whi ...
* Multifocal motor neuropathy
* Axillary neuropathy
* Long thoracic neuropathy
* Suprascapular neuropathy
* Toxic neuropathies
* Drug-induced neuropathies
*
Complex Regional Pain Syndrome
Complex regional pain syndrome (CRPS) is any of several painful conditions that are characterized by a continuing (spontaneous and/or evoked) regional pain that is seemingly disproportionate in time or degree to the usual course of any known trau ...
(CRPS)
Plexus disorders:
*
Neuralgic Amyotrophy (idiopathic brachial plexitis)
* Traumatic
brachial plexopathy
A brachial plexus injury (BPI), also known as brachial plexus lesion, is an injury to the brachial plexus, the network of nerves that conducts signals from the spinal cord to the shoulder, arm and hand. These nerves originate in the fifth, sixth, s ...
*
Lumbosacral radiculopathy
Sciatica is pain going down the leg from the lower back. This pain may go down the back, outside, or front of the leg. Onset is often sudden following activities like heavy lifting, though gradual onset may also occur. The pain is often described ...
*
Hirayama disease
Monomelic amyotrophy (MMA) is a rare motor neuron disease first described in 1959 in Japan. Its symptoms usually appear about two years after adolescent growth spurt and is significantly more common in males, with an average age of onset between 1 ...
Root disorders:
* Cervical, thoracic, lumbar, sacral
radiculopathy
Radiculopathy, also commonly referred to as pinched nerve, refers to a set of conditions in which one or more nerves are affected and do not work properly (a neuropathy). Radiculopathy can result in pain (radicular pain), weakness, altered sensati ...
*
Spinal stenosis
*
Arachnoiditis
Arachnoiditis is an inflammatory condition of the arachnoid mater or 'arachnoid', one of the membranes known as meninges that surround and protect the nerves of the central nervous system, including the brain and spinal cord. The arachnoid can be ...
* Leptomeningeal disorders
Motor neuron disease
*
Amyotrophic lateral sclerosis
Amyotrophic lateral sclerosis (ALS), also known as motor neuron disease (MND) or Lou Gehrig's disease, is a neurodegenerative disease that results in the progressive loss of motor neurons that control voluntary muscles. ALS is the most comm ...
*
West Nile virus
West Nile virus (WNV) is a single-stranded RNA virus that causes West Nile fever. It is a member of the family ''Flaviviridae'', from the genus ''Flavivirus'', which also contains the Zika virus, dengue virus, and yellow fever virus. The virus ...
*
Poliomyelitis
Poliomyelitis, commonly shortened to polio, is an infectious disease caused by the poliovirus. Approximately 70% of cases are asymptomatic; mild symptoms which can occur include sore throat and fever; in a proportion of cases more severe sym ...
* Kennedy’s syndrome (
Spinobulbar muscular atrophy
Spinal and bulbar muscular atrophy (SBMA), popularly known as Kennedy's disease, is a debilitating neurodegenerative disorder resulting in muscle cramps and progressive weakness due to degeneration of motor neurons in the brainstem and spinal cor ...
).
History
The first documented experiments dealing with EMG started with
Francesco Redi
Francesco Redi (18 February 1626 – 1 March 1697) was an Italian physician, naturalist, biologist, and poet. He is referred to as the "founder of experimental biology", and as the "father of modern parasitology". He was the first person to cha ...
’s works in 1666. Redi discovered a highly specialized muscle of the electric ray fish (
Electric Eel) generated electricity. By 1773, Walsh had been able to demonstrate that the eel fish’s muscle tissue could generate a spark of electricity. In 1792, a publication entitled ''De Viribus Electricitatis in Motu Musculari Commentarius'' appeared, written by
Luigi Galvani
Luigi Galvani (, also ; ; la, Aloysius Galvanus; 9 September 1737 – 4 December 1798) was an Italian physician, physicist, biologist and philosopher, who studied animal electricity. In 1780, he discovered that the muscles of dead frogs' legs ...
, in which the author demonstrated that electricity could initiate muscle contraction. Six decades later, in 1849,
Emil du Bois-Reymond discovered that it was also possible to record electrical activity during a voluntary muscle contraction. The first actual recording of this activity was made by
Marey in 1890, who also introduced the term electromyography. In 1922, Gasser and
Erlanger used an
oscilloscope
An oscilloscope (informally a scope) is a type of electronic test instrument that graphically displays varying electrical voltages as a two-dimensional plot of one or more signals as a function of time. The main purposes are to display repetiti ...
to show the electrical signals from muscles. Because of the stochastic nature of the myoelectric signal, only rough information could be obtained from its observation. The capability of detecting electromyographic signals improved steadily from the 1930s through the 1950s, and researchers began to use improved electrodes more widely for the study of muscles. The AANEM was formed in 1953 as one of several currently active medical societies with a special interest in advancing the science and clinical use of the technique. Clinical use of surface EMG (sEMG) for the treatment of more specific disorders began in the 1960s. Hardyck and his researchers were the first (1966) practitioners to use sEMG. In the early 1980s, Cram and Steger introduced a clinical method for scanning a variety of muscles using an EMG sensing device.
![Erv EMG](https://upload.wikimedia.org/wikipedia/commons/e/e8/Erv_EMG.jpg)
Research began at the Mayo Clinic in Rochester, Minnesota under the guidance of Dr
Edward H. Lambert, MD, PhD (1915–2003) in the early 1950s. Dr Lambert, known as the "Father of EMG," with the assistance of his Research Technician, Ervin L Schmidt, a self taught electrical engineer, developed a machine that could be moved from the EMG Lab, and was relatively easy to use. As oscilloscopes had no “store” or “print” features at the time, a Polaroid camera was affixed to the front on a hinge. It was synchronized to photo the scan. Fellows studying at Mayo soon learned that this was a tool they wanted, too. As Mayo has no interest in marketing their inventions, Mr. Schmidt went on to continue to develop them in his basement for decades, selling them under the name ErMel Inc.
It was not until the middle of the 1980s that integration techniques in electrodes had sufficiently advanced to allow batch production of the required small and lightweight instrumentation and amplifiers. At present, a number of suitable amplifiers are commercially available. In the early 1980s, cables that produced signals in the desired microvolt range became available. Recent research has resulted in a better understanding of the properties of surface EMG recording. Surface electromyography is increasingly used for recording from superficial muscles in clinical or
kinesiological protocols, where intramuscular electrodes are used for investigating deep muscles or localized muscle activity.
There are many applications for the use of EMG. EMG is used clinically for the diagnosis of neurological and neuromuscular problems. It is used diagnostically by gait laboratories and by clinicians trained in the use of biofeedback or ergonomic assessment. EMG is also used in many types of research laboratories, including those involved in
biomechanics, motor control, neuromuscular physiology, movement disorders, postural control, and
physical therapy
Physical therapy (PT), also known as physiotherapy, is one of the allied health professions. It is provided by physical therapists who promote, maintain, or restore health through physical examination, diagnosis, management, prognosis, patient ...
.
Research
EMG can be used to sense
isometric
The term ''isometric'' comes from the Greek for "having equal measurement".
isometric may mean:
* Cubic crystal system, also called isometric crystal system
* Isometre, a rhythmic technique in music.
* "Isometric (Intro)", a song by Madeon from ...
muscular activity where no movement is produced. This enables definition of a class of subtle motionless gestures to control interfaces without being noticed and without disrupting the surrounding environment. These signals can be used to control a prosthesis or as a control signal for an electronic device such as a mobile phone or PDA .
EMG signals have been targeted as control for flight systems. The Human Senses Group at the
NASA Ames Research Center at
Moffett Field, CA seeks to advance man-machine interfaces by directly connecting a person to a computer. In this project, an EMG signal is used to substitute for mechanical joysticks and keyboards. EMG has also been used in research towards a "wearable cockpit," which employs EMG-based
gestures
A gesture is a form of non-verbal communication or non-vocal communication in which visible bodily actions communicate particular messages, either in place of, or in conjunction with, speech. Gestures include movement of the hands, face, or ot ...
to manipulate switches and control sticks necessary for flight in conjunction with a goggle-based display.
Unvoiced or silent speech recognition recognizes speech by observing the EMG activity of muscles associated with speech. It is targeted for use in noisy environments, and may be helpful for people without
vocal cords
In humans, vocal cords, also known as vocal folds or voice reeds, are folds of throat tissues that are key in creating sounds through vocalization. The size of vocal cords affects the pitch of voice. Open when breathing and vibrating for speech ...
, with
aphasia
Aphasia is an inability to comprehend or formulate language because of damage to specific brain regions. The major causes are stroke and head trauma; prevalence is hard to determine but aphasia due to stroke is estimated to be 0.1–0.4% in th ...
, with
dysphonia, and more.
EMG has also been used as a control signal for computers and other devices. An interface device based on an EMG Switch can be used to control moving objects, such as
mobile robots
A mobile robot is an automatic machine that is capable of locomotion.Hu, J.; Bhowmick, P.; Lanzon, A.,Group Coordinated Control of Networked Mobile Robots with Applications to Object Transportation IEEE Transactions on Vehicular Technology, 2021 ...
or an
electric wheelchair
A motorized wheelchair, powerchair, electric wheelchair or electric-powered wheelchair (EPW) is a wheelchair that is propelled by means of an electric motor (usually using differential steering) rather than human power, manual power. Motorized wh ...
. This may be helpful for individuals that cannot operate a joystick-controlled wheelchair. Surface EMG recordings may also be a suitable control signal for some interactive video games.
In 1999 an EMG program called Echidna was used to enable a man with locked-in syndrome to send a message to a computer. That program, now called NeuroSwitch, developed by Control Bionics enables people with severe disabilities to communicate by text, email, SMS, computer-generated voice and to control computer games and programs, and - through the internet - Anybots telepresence robots.
A joint project involving
Microsoft
Microsoft Corporation is an American multinational technology corporation producing computer software, consumer electronics, personal computers, and related services headquartered at the Microsoft Redmond campus located in Redmond, Washing ...
, the
University of Washington
The University of Washington (UW, simply Washington, or informally U-Dub) is a public research university in Seattle, Washington.
Founded in 1861, Washington is one of the oldest universities on the West Coast; it was established in Seattle a ...
in
Seattle
Seattle ( ) is a seaport city on the West Coast of the United States. It is the seat of King County, Washington. With a 2020 population of 737,015, it is the largest city in both the state of Washington and the Pacific Northwest regio ...
, and the
University of Toronto
The University of Toronto (UToronto or U of T) is a public research university in Toronto, Ontario, Canada, located on the grounds that surround Queen's Park. It was founded by royal charter in 1827 as King's College, the first institution ...
in
Canada
Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...
has explored using muscle signals from hand gestures as an interface device. A
patent
A patent is a type of intellectual property that gives its owner the legal right to exclude others from making, using, or selling an invention for a limited period of time in exchange for publishing an enabling disclosure of the invention."A p ...
based on this research was submitted on June 26, 2008.
In 2016 a startup called Emteq Labs launched a virtual reality headset with embedded EMG sensors for measuring facial expressions. In September 2019 Facebook bought a startup called CTRL-labs that was working on EMG
See also
*
Chronaxie
Chronaxie is the minimum time required for an electric current double the strength of the rheobase to stimulate a muscle or a neuron. Rheobase is the lowest intensity with indefinite pulse duration which just stimulated muscles or nerves. Chronaxi ...
*
Compound muscle action potential
The compound muscle action potential (CMAP) or compound motor action potential is an electromyography investigation (electrical study of muscle function).
The CMAP idealizes the summation of a group of almost simultaneous action potentials from se ...
*
Electrical impedance myography
Electrical impedance myography, or EIM, is a non-invasive technique for the assessment of muscle health that is based on the measurement of the electrical impedance characteristics of individual muscles or groups of muscles. The technique has been ...
*
Electrical muscle stimulation
*
Electrodiagnostic medicine
Electrodiagnosis (EDX) is a method of medical diagnosis that obtains information about diseases by passively recording the electrical activity of body parts (that is, their natural electrophysiology) or by measuring their response to external elect ...
*
Electromyoneurography
Electromyoneurography (EMNG) is the combined use of electromyography and electroneurography This technique allows for the measurement of a peripheral nerve’s conduction velocity upon stimulation (electroneurography) alongside electrical recordi ...
*
Magnetomyography
Magnetomyography (MMG) is a technique for mapping muscle activity by recording magnetic fields produced by electrical currents occurring naturally in the muscles, using arrays of SQUIDs (superconducting quantum interference devices). It has a bette ...
*
Nerve conduction study
A nerve conduction study (NCS) is a medical diagnostic test commonly used to evaluate the function, especially the ability of electrical conduction, of the motor and sensory nerves of the human body. These tests may be performed by medical specia ...
*
Neuromuscular ultrasound
Neuromuscular ultrasound refers to a field in medicine in which ultrasound is used to diagnosis and guide treatment for people with neuromuscular diseases. Neuromuscular ultrasound is often combined with electrodiagnosis, and particularly nerve c ...
*
Phonomyography
Phonomyography (PMG) (also known as acoustic myography, sound myography, vibromyography, and surface mechanomyogram) is a technique to measure the force of muscle contraction by recording the low frequency sounds created during muscular activity.
...
References
Further reading
* Piper, H.: ''Elektrophysiologie menschlicher Muskeln''. Berlin, J. Springer, 1912.
External links
MedlinePlus entry on EMGdescribes EMG
American Association of Neuromuscular & Electrodiagnostic MedicineRisks in Electrodiagnostic Medicine
{{Authority control
Diagnostic neurology
Electrodiagnosis
Electrophysiology
Neurophysiology
Neurotechnology